Rotationally retractable propeller

ABSTRACT

The present invention relates to a retractable thruster for a surface or submersible vessel, the thruster comprising a propulsion assembly comprising a rigid structure secured to a cylindrical turbine, said rigid structure containing or being suitable for containing a motor, said motor being suitable for rotating at least one propeller inside said turbine via at least one rotary shaft between said motor and said propeller, and preferably further comprising a plate for closing the hull placed beneath said turbine and secured thereto, said propulsion assembly being displaceable by displacement means between a retracted position in which it is at rest inside the hull and a deployed position for providing propulsion in which the propeller is immersed beneath the hull. According to the present invention, said displacement means enable said propulsion assembly to be moved between said retracted and deployed positions by said propulsion assembly performing uniform circular movement about an axis of rotation situated substantially at the level of said hull or beneath said hull.

The present invention relates to a thruster that can be retracted intothe hull of a surface or submersible vessel.

BACKGROUND OF THE INVENTION

The thruster is particularly intended for installing on the bow and/orthe stern of a boat. The function of such thrusters is to provide thrustthat is lateral or longitudinal depending on the disposition of thepropeller axis relative to the longitudinal direction of the vessel.They enable propulsion to be applied in both directions, therebyenabling a vessel to move omnidirectionally, particularly whilemaneuvering, and while correcting drift due to wind and current or toresidual way.

More particularly, the present invention relates to a retractablethruster for a surface or submersible vessel, the thruster comprising apropulsion assembly comprising a rigid structure containing or suitablefor containing a motor driving in rotation at least one propeller placedinside a turbine, via at least one rotary shaft between said motor andsaid propeller, and preferably a hull closure plate placed beneath saidturbine and secured thereto, said propulsion assembly being movable bydisplacement means between a rest, position A retracted inside the hull,and a deployed position B for propulsion, in which the propeller isimmersed beneath the hull.

The propeller axis is generally perpendicular to the axis of the motor,and the motor co-operates with the propeller via a geared angle take-offdevice comprising a first rotary shaft extending a motor shaft situatedon the axis of the motor, said first rotary shaft rotating a secondshaft perpendicular to said first rotary shaft and having the propellermounted thereon.

The angle take-off device, also referred to as a “shoulder”, is thusessentially contained in the turbine.

In known manner, the angle take-off device comprises a casing containingtwo shafts rotating respectively about two perpendicular axes ofrotation, and comprising both a first shaft rotated directly orindirectly by said motor and a second shaft driving at least onepropeller in rotation, together with mechanical elements such as gearingmade up of gearwheels, ball bearings, or smooth bearings, therebyenabling rotation to be transmitted from said first shaft to said secondshaft.

Casings of the above type are described in French patent No. 2 798 184in the name of the Applicant.

The first rotary shaft rotated at its top end by a motor can co-operatein the angle take-off device with one or two perpendicular shafts eachrotating a propeller having an axis of rotation extending in the samedirection perpendicular to said first rotary shaft(s). When the thrusteris provided with two propellers in known manner, the first propeller isa traction propeller boosting the second propeller which is a propulsionpropeller, and vice versa by reversing the direction of rotation,providing an assembly that is very effective and that provides thrustsymmetrically in both directions.

Retractable thrusters are described in the following patents: FR 2 652559, FR 2 741 854, and EP 0 863 837.

A retractable thruster includes a device for retracting and extendingthe propeller relative to the hull.

In EP 0 863 837, a displacement device is described deliveringrectilinear up and down movement to the propulsion assembly, enablingthe propeller to be retracted into a well within the hull or to beextended beneath the hull. A transverse “antitorque” or “antirotation”plate secured to the thruster is situated inside the well and is ofshape complementary to the well so as to prevent the thruster fromturning relative to the boat while delivering thrust, where such turningcan be the result of a torque effect, hence the term “antitorque plate”.The device described in EP 0 863 837 also includes means for preventingthe thruster becoming jammed or wedged in its rectilinear up and downmovements.

The devices for moving the propulsion assembly as described in EP 0 863837 present a major drawback, namely the rectilinear displacement of thepropulsion assembly within the hull occupies a large volume therein.

In FR 2 652 559, proposals are made for a deformably rotatabletrapezoidal device generating rectilinear extension or retractionmovement of the propulsion assembly out from or into a well that enablesthe total volume needed for the thruster to be reduced, particularly inthe height direction. Nevertheless, that trapezoidal device with itsasymmetrically pivoting arms co-operating with a bracket secured to theturbine enables the propeller axis to be moved in rectilinear mannerwhile the propeller is being extended from or retracted into the well,thus enabling the propeller to be cleared immediately by putting themechanism into action.

The device for retracting and extending the thruster as described in FR2 652 559 reduces the space occupied by the thruster, particularly in avertical direction, since the thruster can be disposed in inclinedmanner inside the hull and can be deployed outside the hull whileremaining inclined.

Devices are also known for retracting and extending the propulsionassembly in which the propeller is cleared not by imparting verticalrectilinear movement to the propeller axis, but by imparting circularmovement by pivoting the propulsion assembly about a stationary pivotshaft situated at some height inside the hull. In that device, thepropulsion assembly is like a swinging arm with the propeller at its endbeing moved through a circular movement relative to the pivot shaft atthe opposite end of said arm.

It is necessary to extend part of the “arm” outside the hull in order toenable the propeller to be fully extended, thus requiring an opening inthe hull that is greater than that needed merely for passing theturbine. That large opening involves large volumes and weight of waterbeing displaced or contained that are excessive and that endanger themechanical reliability of the propulsion system as a whole, while alsoincreasing the weight at the bow end of the vessel in disadvantageousmanner.

OBJECTS AND SUMMARY OF THE INVENTION

The object of the present invention is to provide a thruster with adevice for retracting and extending the propeller relative to the hullthat combines the advantages of the various devices described in theprior art without presenting the drawbacks thereof.

More particularly, the object of the present invention is to provide adevice for retracting and extending the thruster:

which is mechanically reliable, in particular which avoids phenomena ofjamming or wedging while it is in movement; and

which enables the propeller to be cleared quickly from the well insidethe hull while also making it possible to implement an opening in thehull that is as small as possible.

More particularly, another object of the present invention is to providea thruster including a device for retracting and extending thepropulsion assembly that requires a minimum number of components andthat is easy to assemble, install on the vessel, and to maintain.

Until now, it has been thought that these two requirements implyproviding vertical rectilinear movement to the propeller axis, eventhough systems proposed in the prior art for imparting verticalrectilinear movement to the propeller axis imply either complexmechanical implementation as in FR 2 652 559, or occupy a large amountof volume inside the hull as in EP 0 863 837, i.e. the drawbacks due tothe volume occupied in particular by the displacements of the movingparts through the submerged part of the hull.

That is why another object of the present invention is to provide adevice for retracting and extending the thruster that also makes itpossible to reduce the total volume needed by the thruster, inside thehull, in particular in a vertical direction.

To do this, the present invention provides a retractable thruster for asurface or submersible vessel, the thruster comprising a propulsionassembly comprising a rigid structure secured to a cylindrical turbine,said rigid structure containing or being suitable for containing amotor, said motor being suitable for rotating at least one propellerinside said turbine via at least one rotary shaft between said motor andsaid propeller, and preferably further comprising a plate for closingthe hull placed beneath said turbine and secured thereto, saidpropulsion assembly being displaceable by displacement means between aretracted position in which it is at rest inside the hull and a deployedposition for providing propulsion in which the propeller is immersedbeneath the hull, wherein said displacement means enable said propulsionassembly to be moved between said retracted and deployed positions bysaid propulsion assembly performing uniform circular movement about anaxis of rotation situated substantially at the level of said hull orbeneath said hull.

More particularly, said displacement means comprise guide elementssuitable for co-operating with said propulsion assembly to enable saidpropulsion assembly to be moved between said retracted and deployedpositions (A, B) by said propulsion assembly describing said uniformcircular movement about said axis of rotation situated substantiallylevel with said hull or beneath said hull, said uniform circularmovement being determined by the shape of said guide elements.

The term “uniform circular movement of the propulsion assembly” is usedto mean that all points of said propulsion assembly move simultaneouslyat the same angular speed, circularly about a common axis of rotation,such that that propulsion assembly is subjected to no significantmovement relative to the main movement of circularly displacing itscenter of gravity or any other point thereof. In particular, thepropulsion assembly does not pivot about itself since it does notinclude any stationary element, and in particular it does not includeany member physically embodying the axis of rotation.

Placing the axis of rotation of said propulsion assembly level with thehull or outside it enables the closure plate and the propulsion assemblysecured thereto via the turbine to be cleared immediately from theopening in the hull by a movement that is circular while also enablingthe opening in the hull to be as small as possible.

The optimum effectiveness of an axis of rotation that is not physicallyembodied occurs when said axis of rotation is situated ideally on theoutside skin of the hull or beneath it, so that there is no point of theclosure plate that moves towards the inside of the hull while thepropulsion assembly is being deployed. Nevertheless, in practice, giventhe operating clearance for the closure plate relative to its housing inthe opening in the hull, and in particular relative to an optionalperipheral rabbet around the opening in the hull, it is acceptable forthe axis of rotation to be located slightly above the level of the hull.

The term “level of the hull” is used to mean the level of the continuoussurface of the hull that is in direct contact with the water when saidvessel is floating on the surface of the water, and not the level of anyindentations or housings that might be formed in the hull and that arenot in contact with the water when the vessel is floating on the surfaceof the water.

The term “substantially at the level of the hull” is thus used herein tomean that the center of rotation may be situated slightly above theinside level of the hull, in particular at a height that corresponds tonot more than 50% of the diameter of the cylindrical turbine, and moreparticularly, in practice, a few centimeters above the hull, i.e. a fewcentimeters into the inside volume of the hull, and more particularlystill up to 10 centimeters (cm) above the inside level of the hull.

In addition, because said axis of rotation is not physically embodied,the propulsion assembly is not secured to a pivot shaft.

From a mechanical point of view, the absence of shaft elements embodyingthe axis of rotation of the moving propulsion assembly, and because saidcircular movement is generated by guide elements, i.e. because there areno link arms and in particular no pivot arms providing linkage betweensaid axis of rotation and said propulsion assembly, the operation andthe implementation of the device for displacing the thruster isguaranteed to be reliable and simple in operation. This configurationalso makes it possible to simplify putting the thruster into place whileit is being installed on the vessel and obtaining ideal positioning ofthe thruster in the hull.

Deploying said propulsion assembly by moving it in rotation enables itto be placed in an inclined manner inside the volume of the hull bothwhen it is in the retracted position and when it is in the deployedposition, such that, overall, the volume needed for said thruster insidethe hull, particularly in the height direction, can be less thanthree-fourths the volume needed by a conventional retractable thrusterthat is deployed by a vertical rectilinear movement. The term “inclinedposition” is used herein to mean that the longitudinal axis of saidrigid structure perpendicular to the transverse axis of said turbine isinclined and/or that the axial plane of symmetry including the or bothrotary shafts is inclined.

It will be understood that said closure plate closes said orifice in thehull when said propulsion assembly is in the retracted position. It willalso be understood that the shape of said “trap door” reproduces theshape of the hull, thus ensuring proper compliance with hydrodynamicrelationships so as to eliminate any sources of parasitic turbulence.

In a preferred embodiment of the thruster of the invention, said guideelements comprise at least one moving first guide element secured tosaid propulsion assembly describing the same uniform circular movementas said propulsion assembly and suitable for co-operating with at leastone stationary second guide elements secured to said hull, said uniformcircular movement being imposed by the shape of said guide elements,said first and second guide elements co-operating by displacement ofsaid first guide element relative to said second guide element in orderto enable said propulsion assembly to be moved between said retractedand deployed positions (A, B).

The term “secured to the hull” is used herein to mean that when saidpropulsion assembly is installed inside the hull of the vessel, inparticular by being included in a caisson supporting the propulsionassembly and fitted to the top edge of a well, itself fitted inside saidhull and having a base surrounding said opening in the hull, said secondguide elements are secured to the walls of said caisson and, whereappropriate, to the walls of said well, i.e. to the hull itself of thevessel.

This implementation enables said guide elements also to perform afunction of supporting said propulsion assembly and/or a function ofproviding a connection between said propulsion assembly and the hullSaid second guide element may be supported, in particular by a structuresecured to said hull. The connection between said propulsion assemblyand said first moving guide element prevents any substantial movement ofsaid propulsion assembly relative to said first guide element andenables the circular movement of the propulsion assembly to be uniform.The circular trajectory of the movement of the propulsion assembly isimposed by the respective shapes of said first and second guideelements, thus making said movement mechanically reliable and simple toimplement.

In a more particular embodiment, said moving first guide element isconstituted by a male part forming a slider and secured to saidpropulsion assembly, and said second guide element is constituted by afemale part forming a slideway, said slideway forming a circular arcenabling said first guide element to describe said circular movementinside said second guide element.

In an inverse embodiment, said moving first guide element secured tosaid propulsion assembly is constituted by a slideway-forming femalepart and said second guide element is constituted by a slider-formingmale part, said slideway forming a circular arc enabling said secondguide element to describe said circular movement inside said first guideelement.

It will be understood that said first and second guide elementsconstituted by said male and female parts form complementary parts thatco-operate with each other to provide guidance. Said slideway may beconstituted by guide rails, notches, or perforations, and the slider(s)may be constituted by elements of finger shape, or in a variant bywheels. It is the shape of the slideway which defines the trajectory ofsaid circular movement and the male slider-forming part constitutes aguided element. Thus, amongst said first and second guide elements,there are both guided elements (referred to above as the male part) andguiding elements (referred to above as the female part).

Also advantageously, and as mentioned above, said propulsion assembly isincluded in part inside a caisson and is secured thereto, said caissonbeing fitted on the top edge of a well, itself fitted inside said hulland having its base surrounding said opening in said hull. Moreparticularly, said caissons and wells have side walls defining a spacethat is substantially in the form of a rectangular parallelepiped.

In an advantageous embodiment and in order to reduce the volume occupiedinside the hull, said propulsion assembly is inclined in such a mannerthat a plane containing the longitudinal axis of said rigid structurecontaining said rotary shaft is inclined in the retracted position (A)relative to the junction plane between said caisson and said well at anangle α of value lying in the range 10° to 60°, preferably in the range10° to 30°, and is inclined in the deployed position (B) relative to thesame junction plane at an angle β of value lying in the range 45° to100°, and preferably in the range 60° to 90°.

In a preferred embodiment, said guide elements comprise a plurality ofsaid first and second guide elements disposed laterally on either sideof said propulsion assembly on either side of a vertical planecontaining the longitudinal axis of said rigid structure.

Said guide elements may comprise a plurality of sliders disposed oneither side of said propulsion assembly and co-operating with aplurality of slideways disposed on either side of said propulsionassembly, said slideways being secured to said hull.

The term “plurality” is used herein to mean that said first and secondguide elements comprise at least two said first guide elements and atleast two said second guide elements, with at least one of said firstguide elements or at least one said second guide elements on either sideof said propulsion assembly.

Still more particularly, said second guide element(s) is/are included inor associated with one or more plates mounted in stationary manner on aside wall of said caisson, or on opposite side walls of said caisson.

In a preferred embodiment, said first guide elements comprise at leastthree male parts, preferably three sliders disposed in a triangle,symmetrically on either side of said propulsion assembly so as toco-operate respectively with at least two slideway-forming female partsdefining concentric circular arcs that are geometrically similar anddisposed symmetrically on either side of said propulsion assembly, atleast two of said male parts, preferably said sliders, being suitablefor sliding inside a first slideway of greater radius and at least onethird male part, preferably a third slider, being suitable for slidinginside at least one second slideway of smaller radius.

The term “geometrically similar” is used herein to mean that the twocircular arcs occupy the same angular sector.

This embodiment provides guidance to the propulsion assembly in highlyeffective manner, conferring mechanical reliability and stiffness whilethe assembly is set into movement, while also being very simple toimplement.

This embodiment also ensures good mechanical stability to counter thetorque effect generated by propulsion when the thruster is in a stage ofactively delivering thrust, thereby making it possible to avoid thefatigue stresses that are usually encountered on retractable thrustersand to conserve satisfactory or even exact coincidence between theopening in the hull and the trap door for closing the opening, therebyensuring that the hull of the boat retains its hydrodynamic performancein full.

Advantageously, said guide elements co-operate with drive means enablingsaid circular movement of the propulsion assembly relative to the hullto be generated.

Still more particularly, said first or second guide element is turnedrelative to said second or first guide element in a said circularmovement by a motor co-operating, where appropriate, with said first orsaid second guide element via link elements in such a manner as toenable said propulsion assembly to be blocked in the retracted position(A) or in the deployed position (B), where appropriate.

It will be understood that it is advantageous to turn the elementsforming the male part regardless of whether they constitute the first orthe second guide elements by making them co-operate via said linkelements with drive means.

Finally, in a particular embodiment, said rigid structure comprises astructure in the form of a rectangular parallelepiped providing aleaktight connection firstly with a cover covering said motor, andsecondly with said turbine, said first guide elements being mountedagainst opposite side faces of said rectangular structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention appear inthe light of the following detailed description of an embodiment givenwith reference to the accompanying figures, in which:

FIGS. 1A and 1B are perspective views of the inside of the hull with athruster integrated in a caisson and a well, said propulsion assembly(without its propeller) being shown in its retracted position inside thehull in FIG. 1A and in its deployed position outside the hull in FIG.1B;

FIGS. 2A and 2B are views corresponding to FIGS. 1A and 1B respectivelywith the caisson that supports the propulsion assembly being removed soas to show only the well situated above the opening in the hull togetherwith the position of the propulsion assembly (without its propeller)when in the retracted position (FIG. 2A) and in the deployed position(FIG. 2B);

FIG. 3 is an exploded view showing the various component elements of thethruster in the hull together with the propulsion assembly;

FIGS. 4A, 4B, and 4C are diagrammatic longitudinal section views on theaxis of the boat showing a thruster of the invention in the retractedposition (FIG. 4A), in the intermediate position (FIG. 4B), and in thedeployed position (FIG. 4C);

FIGS. 5A, 5B, and 5C show the propulsion assembly in longitudinal viewin the positions of FIGS. 4A, 4B, and 4C, respectively;

FIG. 6 is a longitudinal section view of a thruster comprising apropulsion assembly integrated in a caisson and a well in the hull of aboat;

FIG. 7 is a cross-section view on A-A of FIG. 6; and

FIGS. 8A and 8B show a variant embodiment of a slider of the invention.

MORE DETAILED DESCRIPTION

The propulsion assembly 1 of the invention comprises a closed andleaktight rigid structure 2, 2 ₁ secured to a tubular turbine 4.

Said rigid structure 2, 2 ₁ contains a motor (not shown) and a rotaryshaft (not shown) for rotating at least one propeller 3, the propeller 3being contained inside a tubular duct to constitute said turbine 4.

Said rigid structure 2, 2 ₁ is constituted by a structure 2 in the formof a rectangular parallelepiped constituting a box having four solidfaces defining a rectangular parallelepiped with an open face at one endthat is secured in leaktight manner to the tubular duct of the turbine4, and having an open face at its opposite end providing a leaktightconnection with a rectangular cover 2 ₁ covering the motor of thepropulsion assembly and the turbine 4.

The rectangular structure 2 defines a column presenting a longitudinalaxis of symmetry LL′ corresponding substantially to the axis of the mainrotary shaft which is driven directly by the motor inside the structure2, 2 ₁ and which is connected at its other end to an angle take-offdevice inside the turbine 4, as described below. The tubular structureconstituting the turbine 4 has a transverse axis ZZ′ perpendicular tothe longitudinal axis LL′ of the rectangular structure 2.

The center of the turbine 4 has a shoulder or casing 3, containing anangle take-off device to provide the connection between the main rotaryshaft of the structure 2 extending along the direction ZZ′ and connectedto the motor inside the cover 2 ₁, and one or two rotary shaftsextending in the transverse direction ZZ′ and connected to one or twopropellers 3 contained inside the turbine 4. A first propeller mayoperate in traction boosting a second propeller which operates inthrust, or vice versa when the direction of rotation is reversed. Thistwo-propeller system provides propulsion that is very effective withthrust that is symmetrical in the two opposite directions correspondingto the axis ZZ′ extending transversely to the longitudinal direction LL′of the thrust assembly and to the longitudinal direction XX′ of theboat.

The propulsion assembly 1 is mounted inside a caisson 12 ₁ that issubstantially in the shape of a rectangular parallelepiped andco-operating via a leaktight junction lying in a junction plane 123 witha well 12 ₂ that is substantially in the form of a rectangularparallelepiped and that is made inside the hull, with a cutout 8 beingmade through said hull 7 inside the well. The propulsion assembly 1 issupported by the upper caisson 12 ₁ having lateral walls with a bottomedge 12 ₄ that is fixed in leaktight manner to the top edge 12 ₅ of thelateral walls of the well 12 ₂. The propulsion assembly 1 is secured tothe caisson 12 ₁ but is movable relative thereto, in uniform circularmovement as described below.

Beneath the turbine 4, a closure plate 6 reproducing the shape of thehull co-operates with a rabbet 8 ₁ (FIG. 4B) around the periphery of theopening 8 in the hull 7 so that in the retracted position (FIGS. 2A and4B) the plate 6 is in smooth continuity with the remainder of the hull7. The closure plate 6 is connected to the turbine 4 by support elements6 ₁.

The propulsion assembly 1 of the invention is retractable by means of apivoting device which is described below and which imparts circularmovement for extending it out from the well and the hull or forretracting it into the well by turning about an axis of rotation 11situated at the level of the hull 7 (FIGS. 4A to 4C) and not physicallyembodied by a pivot shaft.

When the propulsion assembly 1 is retracted inside the well 12 ₁, theopening 8 in the hull is automatically closed by the trap door 6 that issecured to the tubular duct of the turbine 4, and the outside shape ofthe trap door reproduces the shape of the hull 7, thus complyingproperly with hydrodynamic relationships and avoiding any source ofparasitic turbulence.

The pivot device for pivoting between a retracted position A inside thehull and a deployed position B for thrust in which the propeller isextended outside the well and projects beyond and beneath the hull 7comprises:

-   -   male guide elements 9 ₁, 9 ₂, 9 ₃ mounted on faces that are        opposite in the transverse direction ZZ′ of the rectangular        rigid structure 2 and providing a junction between the turbine 4        and the cover 2 ₁. More precisely, sliders 9 ₁, 9 ₂, and 9 ₃ are        supported by respective triangular plates 16 mounted on either        side of the rectangular structure 2. These sliders 9 ₁, 9 ₂, and        9 ₃ are placed on the plates 16 in a triangular configuration        and co-operate with slideways formed by circular slots 10 ₁, 10        ₂ provided in support plates 15 placed facing the plates 16.

The two pairs of slideways 10 ₁, 10 ₂ are disposed symmetrically oneither side of said propulsion assembly in co-operation with the sliders9 ₁-9 ₃ supported by the two plates 16, each of which is placed on arespective side of said rigid rectangular structure 2.

The two slideways 10 ₁, 10 ₂ thus constitute female parts thatco-operate with the male parts 9 ₁, 9 ₂, and 9 ₃.

More precisely, the slideways 10 ₁, 10 ₂ define concentric circular arcsthat are geometrically similar, occupying the same angular sector, i.e.inscribed within the same circular section. Still more precisely, afirst slider 9 ₁ is suitable for moving inside the first slideway 10 ₁while the other two sliders 9 ₂, 9 ₃ slide inside a second slideway 10₂, defining an arc situated above the first slideway 10 ₁, and defininga circular arc that is concentric with the first slideway but of largerradius and occupying the same angular sector (geometrically similar).

The plates 15 in which the circular slideways 10 ₁ and 10 ₂ are definedare themselves fixed to opposite side edges of the caisson 12 ₂ viasecond plates 15 ₁. The plates 15 and 15 ₁ are positioned inside thecaisson 12 ₁ in such a manner that the circular slideways 10 ₁ and 10 ₂present a center of circular symmetry that is situated level with thehull 11 (which center corresponds to the center of rotation of thesliders 9 ₁, 9 ₂, and 9 ₃ within the slideways 10 ₁ and 10 ₂, see FIGS.4A and 4B).

The sliders 9 ₁, 9 ₂, and 9 ₃ are constituted by cylindrical fingerssurrounded by bushings 9 ₄ (see FIG. 3) making them easier to slideinside the circularly-arcuate slots constituting the slideways 10 ₁ and10 ₂. In a variant embodiment shown in FIGS. 8A and 8B, the guideelements comprise a single slider 9 of circularly-arcuate shapecorresponding to the slideway that is formed by a circularly-arcuateslot 10. It will be understood that in this FIG. 8 embodiment, it ispossible to envisage the plates 15 ₁ that include the slots 10 beingsecured to the rectangular rigid structure 2 connecting the cover 2 ₁ tothe turbine 4 and to envisage the triangular plates 16 supporting theslider 9 being fixed on the side walls inside the caisson 12 ₁.

It will be understood that the disposition of a plurality of sliders 9₁, 9 ₂, 9 ₃ co-operating with a plurality of slideways 10 ₁ and 10 ₂ inthe first variant embodiment and the form using a single slider 9co-operating with a single slideway 10 (FIG. 8) in the second variantembodiment both enable the propulsion assembly to be moved in uniformcircular manner that is determined by the shape of said guide elements 9₁, 9 ₂, 9 ₃ co-operating with the guide elements 10 ₁, 10 ₂. The term“uniform circular movement” is used herein to mean that the propulsionassembly does not turn other than by its main circular turning movementabout the virtual center of rotation 11 that is defined by the shape ofthe guide elements 9, 9 ₁-9 ₃, and 10, 10 ₁-10 ₂, which present as theircenter of circular symmetry said virtual center of rotation 11 of thepropulsion assembly 1. In other words, the propulsion assembly 1 movesuniformly when it moves circularly. When the propulsion assembly passesfrom the retracted position inside the hull (A, FIG. 4A) to the deployedposition outside the hull (B, FIG. 4C), this uniform circular movementensures that the closure plate 6 immediately clears the opening 8 andallows only the turbine 4 with its propeller 3 to pass therethrough,which explains why the opening 3 can be relatively small in size.

The circular movement of the propulsion assembly 1 inside the slideways10 ₁, 10 ₂ or 10 is imparted by a displacement device comprising:

a motor 13 of the type comprising a motor and gearbox unit co-operatingwith pulleys 13 ₁, 13 ₂ disposed side by side on a common rotary shaftextending in the transverse direction ZZ′ perpendicular to thelongitudinal direction LL′ of the propulsion assembly 1.

Said pulleys 13 ₁, 13 ₂ receive straps 14 ₁, 14 ₂. A first strap 14 ₁referred to as the “down” strap has one end fixed to one of said pulleys13 ₁ and its other end fixed to the top cap 2 ₁. Two second straps 14 ₂referred to as “up” straps provide respective connections between thepulleys 13 ₂ to which they are fixed by one of their ends, and theturbine 4 to which they are fixed by their opposite ends.

The operation of extending or retracting the propulsion assembly iscontrolled from outside the caisson by a hydraulic, electrical, orcompressed air system (not shown) acting on the motor 13. Actuating themotor 13 causes the pulleys 13 ₁ and 13 ₂ to rotate so as to wind out orwind in the down strap 14 ₁ and conversely to wind in or wind out the upstrap 14 ₂, thereby lowering the turbine 4 and thus extending thepropulsion assembly into its deployed position B, or respectivelyraising the turbine 4, and thus enabling the propulsion assembly to bedeployed into position B or retracted into position A inside the hull 7.

The non-reversible nature of the motor 13 ensures that the thruster isblocked either in its retracted position A or in its deployed position Bat the end of winding out or winding in the straps 14 ₁, 14 ₂.

It should be observed that the rigidity imparted to the propulsionassembly of the invention, firstly by said rigid structure 2, andsecondly by the guidance of said propulsion assembly 1 secured to saidmale elements 9 ₁-9 ₃ pivoting within the stationary female elements 10₁, 10 ₂, ensures that the deformation that is normally due to the torqueeffect that is generated during a stage of active propulsion is absent,thus making it possible to avoid the fatigue stresses that are usuallyencountered with retractable thrusters. This rigidity also makes itpossible to conserve exact coincidence between the closing trap door 6and its housing 8-8 ₁ in the underwater portion of the hull 7, thusensuring that the hull 7 of the boat retains its hydrodynamicperformance.

The motor (not shown) of the propulsion assembly, contained inside thecover 2 ₁ may be an electric motor, a compressed air motor, or ahydraulic motor. By its very design, this propulsion assembly 1 is notsubjected to seizing during its movements entering or leaving the well.

Finally, the circular movement of the propulsion assembly makes itpossible to reduce the volume it occupies inside the hull insofar as itenables the assembly to be disposed inside the hull so that it isinclined when in its retracted position A at an angle α relative to thejunction plane 12 ₃ (XOZ) between the caisson 12 ₁ and the well 12 ₂having a value lying in the range 10° to 60°, preferably in the range10° to 30°, and having an angle β in the deployed position B having avalue of 45° to 100°, and preferably lying in the range 60° to 90°relative to the same junction plane (XOZ) that is substantially parallelto the hull.

The design whereby the propulsion assembly is mounted inside the hullsecured to the caisson 12 ₁ makes it easier to position inside the hull.

FIGS. 4A and 4C show an axis of rotation 11 situated at the level of thehull, however the axis could equally well be situated below the hullinsofar as its position makes it possible for the closure plate 6 toclear instantly the rim 8 ₁ of the opening 8 in the hull 7.

1-13. (canceled)
 14. A retractable thruster for a surface or submersiblevessel, the thruster comprising a propulsion assembly comprising a rigidstructure secured to a cylindrical turbine, said rigid structurecontaining or being suitable for containing a motor, said motor beingsuitable for rotating at least one propeller inside said turbine via atleast one rotary shaft between said motor and said propeller, andpreferably further comprising a plate for closing the hull placedbeneath said turbine and secured thereto, said propulsion assembly beingdisplaceable by displacement means between a retracted position in whichit is at rest inside the hull and a deployed position for providingpropulsion in which the propeller is immersed beneath the hull, whereinsaid displacement means enable said propulsion assembly to be movedbetween said retracted and deployed positions by said propulsionassembly performing uniform circular movement about an axis of rotationsituated substantially at the level of said hull or beneath said hull.15. A thruster according to claim 14, wherein said displacement meanscomprise guide elements suitable for co-operating with said propulsionassembly to enable said propulsion assembly to be moved between saidretracted and deployed positions by said propulsion assembly describingsaid uniform circular movement about said axis of rotation situatedsubstantially level with said hull or beneath said hull, said uniformcircular movement being determined by the shape of said guide elements.16. A thruster according to claim 15, wherein said guide elementscomprise at least one moving first guide element secured to saidpropulsion assembly describing the same uniform circular movement assaid propulsion assembly and suitable for co-operating with at least onestationary second guide elements secured to said hull, said uniformcircular movement being imposed by the shape of said guide elements,said first and second guide elements co-operating by displacement ofsaid first guide element relative to said second guide element in orderto enable said propulsion assembly to be moved between said retractedand deployed positions.
 17. A thruster according to claim 16, whereinsaid moving first guide element is constituted by a male part forming aslider and secured to said propulsion assembly, and said second guideelement is constituted by a female part forming a slideway, saidslideway forming a circular arc enabling said first guide element todescribe said circular movement inside said second guide element.
 18. Athruster according to claim 16, wherein said moving first guide elementsecured to said propulsion assembly is constituted by a slideway-formingfemale part and said second guide element is constituted by aslider-forming male part, said slideway forming a circular arc enablingsaid second guide element to describe said circular movement inside saidfirst guide element.
 19. A thruster according to claim 15, wherein saidguide elements comprise a plurality of said first and second guideelements, disposed laterally on either side of said propulsion assemblyon either side of a vertical plane containing the longitudinal axis ofsaid rigid structure containing said rotary shaft extending between saidmotor and said turbine.
 20. A thruster according to claim 14, whereinsaid propulsion assembly is included in part inside a caisson and issecured thereto, said caisson being fitted on the top edge of a well,itself fitted inside said hull and having its base surrounding saidopening in said hull.
 21. A thruster according to claim 20, wherein saidpropulsion assembly is inclined in such a manner that a plane containingthe longitudinal axis of said rigid structure containing said rotaryshaft is inclined in the retracted position relative to the longitudinaldirection XX′ of the surface vessel and/or relative to the junctionplane between said caisson and said well at an angle a of value lying inthe range 100 to 600, preferably in the range 10° to 30°, and isinclined in the deployed position relative to the same longitudinaldirection XX′ of the surface vessel and/or relative to the junctionplane between said caisson and said well at an angle β of value lying inthe range 45° to 100°, and preferably in the range 60° to 90°.
 22. Athruster according to claim 16, wherein said second guide element(s)is/are included in or associated with one or more plates mounted instationary manner on a side wall of said caisson, or on opposite sidewalls of said caisson.
 23. A thruster according to claim 15, whereinsaid first guide elements comprise at least three male parts, preferablythree sliders disposed in a triangle, symmetrically on either side ofsaid propulsion assembly so as to co-operate respectively with at leasttwo slideway-forming female parts defining concentric circular arcs thatare geometrically similar and disposed symmetrically on either side ofsaid propulsion assembly, at least two of said male parts, preferablysaid sliders, being suitable for sliding inside a first slideway ofgreater radius and at least one third male part, preferably a thirdslider, being suitable for sliding inside at least one second slidewayof smaller radius.
 24. A thruster according to claim 14, wherein saidguide elements co-operate with drive means enabling said circularmovement of the propulsion assembly relative to the hull to begenerated.
 25. A thruster according to claim 16, wherein said firstguide elements comprise at least three male parts, preferably threesliders disposed in a triangle, symmetrically on either side of saidpropulsion assembly so as to co-operate respectively with at least twoslideway-forming female parts defining concentric circular arcs that aregeometrically similar and disposed symmetrically on either side of saidpropulsion assembly, at least two of said male parts, preferably saidsliders, being suitable for sliding inside a first slideway of greaterradius and at least one third male part, preferably a third slider,being suitable for sliding inside at least one second slideway ofsmaller radius, and wherein said first or second guide element is turnedrelative to said second or first guide element in a said circularmovement by a motor co-operating, where appropriate, with said first orsaid second guide element via link elements in such a manner as toenable said propulsion assembly to be blocked in the retracted positionor in the deployed position, where appropriate.
 26. A thruster accordingto claim 14, wherein said rigid structure comprises a structure in theform of a rectangular parallelepiped providing a leaktight connectionfirstly with a cover covering said motor, and secondly with saidturbine, said first guide elements being mounted against opposite sidefaces of said rectangular structure.